As speech recognition technology is developed, use of a speech recognition secretarial service which recognizes a speech command generated by a user and executes a corresponding command is being significantly increased. An application scope of the speech recognition secretarial service is expanding from a home application to applications to various fields such as vehicles and the like. That is, in conjunction with speech recognition secretarial service and a telematics service, a speech command generated by a user is transmitted to a vehicle to control the vehicle. Accordingly, the user can lock or unlock a door of the vehicle, or turn on an air conditioner of the vehicle in advance and control a temperature inside the vehicle, among other functions.
In order to use the speech recognition secretarial service as described above, user authentication is required. This is because when user authentication is not performed, an unauthorized person may use a vehicle without permission. In a conventional user authentication method, for example, a password (e.g., a personal identification number (PIN) code) is spoken so that a home speaker 130 can recognize the spoken password. However, such user authentication through a direct production of a password is risky because the password can be exposed to others.